Instantaneous positions of microwave solar bursts: Properties and validity of the multiple beam observations

The multiple beam technique determine burst sources positions when their angular extent are small compared with the beam shapes. We show for the first time that we carl check the above condition with the simultaneous observation using at least four beams. The developed technique is not critically dependent on source shapes. By means of simulations me found that for narrow 1 arcmin long sources the uncertainties in position determination are less than 5 arcsec, and much better for symmetrical sources. The influence of side lobes on source positions determinations was found to be negligible. A qualitative method was developed when data from only three beams are available. Both methods are applied to the analysis of a solar burst observed with multiple beams at 48 GHz with the Itapetinga 13.7 m antenna. The multiple beam technique also offers the unique advantage to determine flux density irrespectively from the position displacements of the source with respect to the beams, or vice versa.140337338

Multi-resolution wavelet analysis of high time resolution millimeter wavelength observations of solar bursts

By means of the wavelet representation of multi-resolution analysis, we study millimeter wavelength (mm-w) radio solar bursts obtained at 48 GHz with high time resolution (less than or equal to8 ms), observed at Itapetinga (Brazil). The multi-resolution analysis decomposes the signal locally both in time and in frequency. allowing us to identify the different temporal structures which underlie the flux density time series and the transient phenomena characteristic of solar bursts. The analysis was applied to the flux time profile of four solar bursts observed at a mm-w, studying separately the pre-flare, impulsive and post-flare phases when possible. We find that a wide range of time scales contributes to the radio flux. The minimum time scale found for the impulsive phase is 32 ms, after which the noise dominates the emission the maximum is 8 s. Pre- and post-flare phases have a minimum time scale of 256 ms and a maximum between 1 to 8 s. Multi-resolution 'spectral indexes', which are a measure of the self-similar behavior of the signal. are in some cases bigger for the impulsive phase than for the pre- and post-flare phases. We find that as the Aux becomes higher the contribution from shorter time scales is enhanced.366131732

Launch of solar coronal mass ejections and submillimeter pulse bursts

The rapid solar spikes (100-500 ms) recently discovered at submillimeter waves bring new possibilities to investigate energetic processes near the solar surface that might have an important role in the launch and propelling of ionized mass away from the Sun. We present a study on the association between the launch time of coronal mass ejections (CMEs) observed by the LASCO instruments on the SOHO spacecraft and the onset of the new kind of rapid solar spikes (100-500 ms) observed at submillimetric waves (212 and 405 GHz) by the new Solar Submm-wave Telescope (SST). We investigated six submm-wave events, all found associated to CMEs. Seven related CME were identified. Five of them were associated with flares with large GOES class soft X-rays, presenting distinct time histories and associations at other energy ranges, and two of them were related to flares behind the solar limb, with simultaneous related activity observed in the visible solar disk. Ultraviolet images from EIT on SOHO show some kind of small or large-scale magnetic activity or brightening for all events. The extrapolation of apparent CME positions to the solar surface show that they occurred nearly coincident in time with the onset of submm-wave pulses for all six events. These results suggest that pulse bursts might be representative of an important early signature of CMEs, especially for events beginning near the center of the solar disk, sometimes identified as 'halo' CMEs. They lead to several challenging questions relative to the physical nature of the pulses and its association to the launch and acceleration of coronal mass ejections. Although these evidences may favor multiple rapid energy releases at the origin near the solar surface, they require further research in order to better understand both diagnostics and model descriptions.O TEXTO COMPLETO DESTE ARTIGO, ESTARÁ DISPONÍVEL À PARTIR DE FEVEREIRO DE 2015.108A

Submillimeter-wave atmospheric transmission at El Leoncito, Argentina Andes

We present the results of one year of daytime atmosphere transmission measurements obtained at 212 and 405 GHz by a 1.5 m solar radio telescope located at El Leoncito site, 2550 m altitude in Argentina Andes. We used three different methods: 1) absolute derivation from strong solar signal at different elevation angles; 2) direct derivation from observed known solar brightness times the antenna coupling factor; and 3) fitting the observed sky emission plots as a function of elevation angle, also known as "tipping." Some differences were found for the transmission determined by the three methods, the most important is that methods 1) and 2) are restricted to smaller values of opacity. Method 1) is restricted to measurements at low elevation angles. Method 2) has the advantage to extend measurements to considerably higher values of attenuation. For the El Leoncito site the correlation of optical depth at 405 and 212 GHz was found (T-405/T-212) = 4.43, smaller than model predictions (approximate to 5.0). Measurements at both frequencies obtained for 319 days in one year indicate that 50% of time 7212 74% zenithal transmission) and T-405 22% transmission), with small seasonal dependence compared to other sites. The opacity related precipitable water vapor is smaller compared to model estimates, suggesting an upper atmosphere water vapor depression, characteristic to the region.5341528153

Properties of fast submillimeter time structures during a large solar flare

We report properties of fast varying submillimeter emission during one of the strongest solar radio flares of solar cycle 23. Emission was obtained by the Solar Submillimeter-Wave Telescope at 212 and 405 GHz and compared with hard X-ray and gamma-ray counts up to few tens of MeV photon energy ranges. We employ different methods to detect and characterize flux density variations and find that during the impulsive phase of the event, the closer in time to the peak. are, the higher the occurrence of the fastest and brightest time structures. The good comparison with hard X-ray and gamma-ray count rates indicates that fast submillimeter pulses are the signatures of primary energetic injections. The characteristics of the fast spikes at 212 and 405 GHz, such as their flux density and localization, compared to those of the underlying slower impulsive component, also suggest that their nature is different.5921158058

Diffuse component spectra of solar active regions at submillimeter wavelengths

Solar maps at 212 and 405 GHz obtained by the Solar Submillimetric Telescope (SST) show regions of enhanced brightness temperature, which coincide with the location of active regions. A statistical study of the radio emission from these active regions was performed for the first time at such high frequencies during 23 days on June and July 2002, when the atmospheric opacity was low. The brightest regions on the maps were chosen for this study, where the brightness excess observed varies from 3 to 20% above quiet Sun levels (i.e., 200-1000 K) at both wavelengths. Sizes of the regions of enhanced emission calculated at half the maximum value were estimated to be between 2' and 7'. These sizes agree with observed sizes of active regions at other wavelengths such as H alpha and ultraviolet. An important result is that the flux density spectra of all sources increase toward submillimeter frequencies, yielding flux density spectral index with an average value of 2.0. The flux density of the active region sources were complemented with that from maps at 17 and 34 GHz from the Nobeyama Radio Heliograph. The resulting spectra at all four frequencies were fit considering the flux density to be due to thermal bremsstrahlung from the active region. In the calculations, the source radius was assumed to be the mean of the measured values at 212 and 405 K. The effective temperatures of the radio emitting source, assumed homogeneous, obtained from this fit were 0.6-2.9 x 10(4) K, for source diameters of 2'-7'.227226528

Evidence that synchrotron emission from nonthermal electrons produces the increasing submillimeter spectral component in solar flares

We investigate the origin of the increasing spectra observed at submillimeter wavelengths detected in the flare on 2 November 2003 starting at 17:17 UT. This flare, classified as an X8.3 and 2B event, was simultaneously detected by RHESSI and the Solar Submillimeter Telescope (SST) at 212 and 405 GHz. Comparison of the time profiles at various wavelengths shows that the submillimeter emission resembles that of the high-energy X rays observed by RHESSI whereas the microwaves observed by the Owens Valley Solar Array (OVSA) resemble that of similar to 50 keV X rays. Moreover, the centroid position of the submillimeter radiation is seen to originate within the same flaring loops of the ultraviolet and X-ray sources. Nevertheless, the submillimeter spectra are distinct from the usual microwave spectra, appearing to be a distinct spectral component with peak frequency in the THz range. Three possibilities to explain this increasing radio spectra are discussed: (1) gyrosynchrotron radiation from accelerated electrons, (2) bremsstrahlung from thermal electrons, and (3) gyrosynchrotron emission from the positrons produced by pion or radioactive decay after nuclear interactions. The latter possibility is ruled out on the grounds that to explain the submillimeter observations requires 3000 to 2x10(5) more positrons than what is inferred from X-ray and gamma-ray observations. It is possible to model the emission as thermal; however, such sources would produce too much flux in the ultraviolet and soft X-ray wavelengths. Nevertheless we are able to explain both spectral components at microwave and submillimeter wavelengths by gyrosynchrotron emission from the same population of accelerated electrons that emit hard X rays and gamma rays. We find that the same 5x10(35) electrons inferred from RHESSI observations are responsible for the compact submillimeter source (0.5 arcsec in radius) in a region of 4500 G low in the atmosphere, and for the traditional microwave spectral component by a more extended source (50 arcsec) in a 480 G magnetic field located higher up in the loops. The extreme values in magnetic field and source size required to account for the submillimeter emission can be relaxed if anisotropy and transport of the electrons are taken into account.245231132

Pulsations at the onset of the great solar burst of 22 October 1989

The onset phase of the 22 October 1989 great solar burst was observed at 48 GHz using the multiple beam technique, which allows unambiguous flux determination irrespective of spatial angular position changes in time. We found strong quasi-periodic pulsating structures as the flux started to rise. Two significantly different time scales of similar to 2.5-4.5 s and similar to 0.2-0.5 s have been observed. These pulsations might be related to magnetohydrodynamic perturbations in the active region. However the fast component also might be a signature of the acceleration and/or injection of energetic electrons.178239340